1. Field of the Invention
The present invention relates to an electrophotographic printing apparatus using a hydrocarbon liquid toner and particularly to a method and article for the elimination of hydrocarbons from printer exhaust.
2. Background of the Art
Hydrocarbon filters are known in the industrial world as effective means for substantially purifying hydrocarbon-laden air that may be the by-product of, for example, industrial processing equipment or automobiles. Most frequently the filters utilize a regenerable carbon adsorbent in large quantities. Such a product is expensive, non-disposable, and may be very heavy, in addition to requiring additional equipment or recycling for regeneration of the filter.
Electrophotography is a well known commercial process and may incorporate the use of either liquid or dry toners. An electrophotographic apparatus that uses liquid toner realizes several advantages over an electrophotographic apparatus that uses dry toner. One such advantage is the achievement of finer resolution prints due to smaller particle size. Because the particles are smaller, a lower mass of toner is required to print to the necessary optical density, reducing the material cost per page. Another advantage is liquid toner""s lack of airborne dry toner particulate (which are known carcinogens). Liquid toner also tends to have a longer shelf life because of increased charge stability as compared to dry toner.
A liquid electrophotographic toner, unlike its dry toner counterparts, contains a significant amount of a hydrocarbon solvent that helps to produce the fine resolution for which liquid toners are preferred. That solvent, however, must be removed from the image at some point in the printing process before the user receives the printed page. Some printer designers choose to evaporate the solvent while the image is still on an intermediate transfer member or on the photoreceptor, and then transferring the substantially dry image to the final substrate. Some manufacturers choose to absorb the solvent from an intermediate transfer member (or photoreceptor) with a specially coated roll. Then typically a beat roll is used to evaporate the absorbed solvent. Still other manufacturers choose to leave the solvent in the image until the image reaches the substrate and then the solvent is evaporated, usually in a fusing step. In any case, the solvent is removed from the image or hardware through evaporation.
Typically, the evaporated solvent is collected in a substantially airtight container and circulated through a condensing unit to condense the solvent back into a liquid. The air that is exhausted is substantially hydrocarbon-free, although some manufacturers will use an additional carbon absorbent filter to ensure exhaust quality. Some of the negative characteristics of the printers that use these solutions include: a bulkier printer to accommodate extra hardware, an increased cost due to extra components, the necessity of a recycling or disposal system for condensed solvent, and the necessity to recycle used carbon filters.
There are significant problems associated with the need to collect all of the airborne hydrocarbons for condensation and disposal. A resolution according to the present invention uses a substantially passive method and article for collecting and disposing of the airborne hydrocarbons simply and in an environmentally-friendly manner.
A method for collecting and disposing of waste airborne hydrocarbons includes providing an air/hydrocarbon mixture as airborne hydrocarbons in either vapor or mist form in an electrophotographic imaging process, directing the air/hydrocarbon mixture to an oleophilic absorbent bed or surface, absorbing the hydrocarbon out of the air/hydrocarbon mixture without necessarily first condensing it. For example, the term xe2x80x9cabsorbing without condensingxe2x80x9d is defined by a test wherein a vapor phase carrying 25% by volume of hydrocarbons at 20xc2x0 C. and 760 mm Hg contacts the absorbent media for no more than three minutes with return flow of the vapor through the media, and at least 50% of the total hydrocarbon is absorbed into the media without having more than 10% by weight of the original hydrocarbon in the vapor phase condense as droplets from the air/hydrocarbon mixture on the media. It is preferred in the practice of the invention, and enabled by the herein described practices to limit condensation under those conditions to less than 5%, less than 3% and even less than 1%, while at the same time removing at least 70% of the original hydrocarbons, at least 80% of the original hydrocarbons, at least 90% of the original hydrocarbons, at least 95% of the original hydrocarbons, and more than 98% or more than 99% of the original hydrocarbons. After removing hydrocarbon from the vapor phase, the process continues by exhausting the reduced hydrocarbon-content air, which can be essentially hydrocarbon-free air, out of the electrophotographic apparatus. There is no need to condense the hydrocarbons as droplets out of the air, because as they pass over and through the bed or cartridge filled with absorbent media, a substantial majority (e.g., at least 80%, preferably at least 90% by weight of the hydrocarbon) is pulled from the air in a gaseous state and captured. The advantage of absorption rather than condensation is that the hydrocarbon, when absorbed, is bound more strongly within the removal system. When merely condensed, the hydrocarbon liquid remains as a flowable liquid lightly attached by surface tension to the surface of the condensing surface. When the flow of air around or through the absorbent cartridge or pod is reduced or stopped, the cartridge or pod may simply be exchanged for another. In a preferred embodiment, the absorbent prevents impermissible toxic leaching (that is leaching of the hydrocarbon solvent from the absorbent) into the environment and might be disposed of in a regular waste stream, such as trash collection and landfill disposal. The absorbent may also have a catalyst, bacteria, or other active ingredient therein that will assist in the breakdown of the ink into environmentally acceptable materials, and/or the absorbent may be additionally hydrophilic.
The absorbent media is referred to as xe2x80x9cnon-leachablexe2x80x9d in preferred practices of the present invention. The term non-leachable has a purpose and a meaning according to the practice of the invention. After absorption of the hydrocarbon has stabilized in the media (that is, after absorption, the media is allowed to sit at room temperature (20xc2x0 C.) and pressure (760 mm Hg) for four hours), the media with 3% by weight hydrocarbon liquid absorbed therein (with at least 50% by weight of the hydrocarbon comprising C10, C11, and C12 linear hydrocarbons, and with less than 5% comprising  less than C8 hydrocarbons) is contacted with deionized water at 30xc2x0 C. for two hours. The term xe2x80x9cnon-leachablexe2x80x9d means that less than 10% by total weight of the absorbed hydrocarbon is leached from the absorbent into the water phase. It is preferred that less than 5% of the absorbed hydrocarbon is absorbed into the water after two hours.
In various embodiments of the method, air (the vapor stream with gaseous hydrocarbon) may be directed to the absorbent with a fan, or pump, for example. Other airflow in the apparatus may be encouraged or introduced through ventilation holes or additional fans. Some manufacturers may choose to control the direction of the airflow with a duct or similar directing means.
Another aspect of the invention is a filter or cartridge for collecting the airborne hydrocarbons. Embodiments of the cartridge will vary in complexity with the amount of vapor to be collected and the type of air direction employed. Some embodiments might simply be a two-part pod comprised substantially of mesh filled with one or more absorbents. Other embodiments include a canister-like cartridge with an inlet and outlet so that hydrocarbon-laden air can be blown or pumped into or through the absorbent(s) therein. In a pod or cartridge that contains very densely packed absorbent(s), it may also be necessary to include air channels or pockets strategically placed throughout the pod or cartridge article.
Many different structural and functional materials may be used in the article. Presumably, cost and weight are factors and such costs are easily managed by using lightweight plastic or even disposable (e.g. cardboard) housing or support materials. It is an aspect of this invention, to effect convenient disposal, and as such, disposable materials are preferred. In the pod-like design, a substantial amount of the available surface area is covered with a mesh or screen, but may include or substitute non-woven cloth (e.g. polyethylene) that may also be oleophilic.
Yet another element of the invention is an oleophilic, non-leaching absorbent for the hydrocarbon solvent. Embodiments of the absorbent include fibrous, porous, particulate, or other structural materials that are oleophilic and will attract and retain hydrocarbons in the structure. For example, such commercial materials as organic fabrics; organic reticulated foams; hydrophobized particles; compacted layers of absorbent materials; non-woven organic fiber structures; and the like may be used.
Examples of commercial materials that have been proven particularly effective that have passed landfill leach testing are Enviro-bond(trademark) 403 absorbent, Imbiber Beads(copyright) absorbent and Bilge Boom(trademark) oil-absorbent sheets. A preferred absorbent is the Imbiber Beads(copyright) absorbent, preferred for its ability to quickly absorb and encapsulate the hydrocarbon solvent without quickly solidifying. In another embodiment, the oleophilic absorbent may be combined with other absorbents, such as hydrophilic absorbents, in order to match the absorbency characteristics of a particular solvent, or to deal with minimal amounts of water vapor or condensation that may appear during venting.